• Immunoassay-Based Microsensing

      Hoying, James; Jabbour, Maurice Elie; Deymier, Pierre; Guzman, Roberto; Barnaby, Hugh; Cuello, Joel (The University of Arizona., 2005)
      Immunoassay systems are recognized as superior modalities for detecting biological substances. Immunoassay sensing offers the advantages of selectivity and sensitivity. Development of a portable micro-immunoassay system is quite desirable for fieldwork applications. The basis of such portable sensing approach would combine molecular printing techniques with solid-state devices. In this work, I report on advances in attaching and patterning antibodies on Si02 substrates with the aim of retaining their biological functionality. The integration of functional antibodies with conventional photodetectors through direct printing onto the oxide layer of the detector will result in a device with on-chip readout. To that effect, monoclonal IgG antibody was printed onto chemically modified and thermally oxidized silicon substrates. Using a generic immunoassay, I was able to validate the activity of the antibody adsorbed on epoxyterminated silane surface coatings. An assay based on Mouse anti-biotin - Biotin conjugated to horseradish peroxidase interaction was used to show the activity of printed antibody, specifically the molecular orientation of the antibody, on the silane-coated surface. In addition, avalanche photodiodes were used as solid-state detector for light detection. Avalanche photodiodes were able to detect the chemiluminescence, an indication of the sensitivity of the sensor for the immunoassay. Furthermore, there were clear differences between 'control' measurements obtained using a saline buffer solution compared to actual measurements obtained from antibody attachment to the surface of the sensor. This difference in signals is an indication that protein-protein interaction 10 occurred. To that effect, on-chip readout, namely in situ measurement of light detection without the aid of additional detector, was shown. In summary, I present, as a proof of concept, one example of immunoassay-based microsensing through the integration of antibody with avalanche photodiodes. This may have potential application in designing commercial, low cost, and portable biosensors.